Roulette settles each accepted selection against the pocket where the ball finishes. A common single-zero wheel has 37 pockets; the rectangular betting layout groups those pockets into numbers, colours, dozens and other selections.
Wheel Numbers, Colours and Zero
Roulette resolves a round when the ball settles in a numbered wheel pocket. A common European wheel has 1 through 36 plus a single zero. A common American wheel adds a double zero. Zero pockets are neither ordinary red nor black numbers, and they affect the outcome of the outside wagers.
The order of numbers around the physical wheel differs from their order on the rectangular betting layout. Neighbours on the wheel are therefore not necessarily adjacent boxes on the layout. That distinction matters for racetrack or neighbour selections, which follow wheel position. Before calculating any example, identify the wheel type and the bet area used. A green zero is not an even-money black result simply because zero is even in arithmetic; the game treats it through its own rules.